Certain alpha,beta-mono-unsaturated aldehydes have heretofore been obtained by the catalytic rearrangement of corresponding tertiary acetylenic carbinols or derivatives thereof. For example, acetylenic carbinols have been converted to unsaturated aldehydes by a process involving initially esterifying the carbinols and then rearranging the ester derivative with the aid of a silver or copper catalyst. Typically, such rearrangement reactions have required several process steps, including the formation of an allene ester intermediate.
In an effort to reduce the number of process steps required for such catalytic rearrangement processes, catalysts derived from a metal of the Vth to VIIth sub-group of the periodic chart, particularly vanadium, niobium, molybdenum, tungsten and rhenium, have been utilized instead of copper or silver catalysts. See British Pat. No. 1,204,754. Such catalysts have permitted acetylenic carbinols to be expeditiously rearranged to unsaturated aldehydes in a single operation. However, the use of such catalysts to the Vth to VIIth sub-group has not been found to be completely satisfactory. Considerable loss of catalyst activity has been found to inevitably occur during the course of the rearrangement reaction. In addition, it has been discovered that decomposition products are formed during the rearrangement reaction as the catalyst loses activity and that these decomposition products cause the aldehyde product to be destroyed as it is formed, thereby reducing product yields.
The catalysts used hitherto for such isomerization reactions have the disadvantage that they are relatively unstable and can only be used once or a few times. In contradistinction thereto the present catalyst system is more stable and useful for a great number of isomerizations. Moreover, the isomerization in the presence of the present catalyst system can be carried out in an advantageous time interval at temperatures between room temperature and about 150.degree. C. This is especially significant in the case of thermolabile starting materials and end products.